The invention refers to a safety device for installation in a gas-supply system, in particular, an acetylene-supply system, where a main pressure regulator relieves gas fed in at inlet pressure to outlet pressure.
In its simplest form, the gas-supply system can be a gas cylinder, a tank or another type of container. Several containers can also be connected to one another, so when one container becomes empty, the system is able to switch to a different container which is still full.
The gas-supply system feeds the gas to a tapping point. The gas to be tapped is pressurized and in this respect already represents a certain hazard potential for users and the environment. In principle, the safety device is suitable for installation in all gas-supply systems of this type. However, it has a particularly beneficial effect when used with combustible or toxic gases, such as methane, propane, natural gas, hydrogen, liquid gas, carbon monoxide, halogens and suchlike, and especially with acetylene-gas-supply systems.
Acetylene (C2H2) is known for being highly flammable and, at high temperature or pressure, decomposes into its elements suddenly if heated. Depending on the circumstances, this decomposition may have a detonating effect, thus endangering people, the surroundings, and the system. Therefore, the maximum operating pressure (outlet pressure) in acetylene extraction lines is usually limited to 1.5 bar of over-pressure. In addition, various safety devices are provided in fittings or piping. These devices are defined, for example, for acetylene systems in general in TRAC 207 (Technische Regeln für Acetylenanlagen und Calciumcarbidlager, “technical rules for acetylene systems and calcium-carbide stores”) and for acetylene manifold systems specifically in standard EN ISO 14114:1999 (Acetylene manifold systems for welding, cutting and allied processes—General requirements).
Safety devices on the inlet-pressure side feature manual or automatic quick-action shut-off devices as per EN ISO 14114:1999, Section 3.6, gas non-return valves, and flashback arrestors. Gas non-return valves prevent the acetylene from flowing back, while flashback arrestors cool down and hold back hot decomposition fumes.
Quick-action shut-off devices are installed in particular in piping or fittings on the inlet-pressure side of the manifold system and shut this off manually or automatically in the event of acetylene decomposition in order to stop the spread of said decomposition even before the main pressure regulator is reached, preventing it from getting through to the outlet-pressure side of the pressure regulator. In line systems where explosions may be expected to start from two sides, such quick-action shut-off devices must be designed in duplicate for both sides accordingly. They are also known as decomposition arrestors and must even be capable of withstanding potential acetylene decomposition when there is a detonative effect, where pressures of over 100 MPa (1000 bar) can occur.